1. Technical Field
The invention relates to a torsional vibration damper for piston engines, particularly for motor vehicle engines, with a hub which can be mounted in a torsionally resistant manner on the crankshaft of the engine, a first flyring which concentrically surrounds the hub and is connected to the outer surface of the hub via a rubber spring device acting in the peripheral direction, as well as a second flyring which is directly or indirectly secured to the hub via a rubber spring device, again acting in the peripheral direction.
2. Prior Art
Known torsional vibration dampers of the aforementioned type, which are mounted directly on the output end of the crankshaft, serve to absorb the engine vibrations induced by forces of inertia. These engine vibrations induced by forces of inertia are in the range of approximately 150 Hz to 650 Hz, depending on design.
In order to cover this entire range, several flyrings capable of motion relative to each other are combined. In a known torsional vibration damper of the aforementioned type (DE-OS 36 08 420), for example, smaller flyrings, mounted in bearings inside the hub, are connected to the main flyring via rubber spring devices.
In known systems, the low-frequency vibrations induced by gas forces, which are in the region of about 40 Hz to 100 Hz, are damped by additional torsional vibration dampers attached to the end of the propeller shaft.
In another known vibration damper (U.S. Pat. No. 3,670,593) the inner flyring is fixed at the hub and the outer flyring is connected with the inner flyring by an additional rubber spring. The rubber springs can be varied in their length and in their properties for the respective task. This known construction only works in a good way if the outer flyring has an essentially lower mass in respect to the inner flyring because otherwise the system can become unstable. Therefore the known vibration damper is very inflexible in respect to the frequencies to be covered and especially there may be difficulties in damping the lower frequency region.